Electrical fuses (eFuses) are used in the semiconductor industry to implement array redundancy, field programmable arrays, analog component trimming circuits, and chip identification circuits. Once programmed, the programmed state of an electrical fuse does not revert to the original state on its own, that is, the programmed state of the fuse is not reversible. For this reason, electrical fuses are called One-Time-Programmable (OTP) memory elements.
The mechanism for programming an electrical fuse is electromigration of a metal semiconductor alloy induced by an applied electrical field and a raised temperature on a portion of the electrical fuse structure. The metal semiconductor alloy is electromigrated under these conditions from the portion of the electrical fuse structure, thereby increasing the resistance of the electrical fuse structure. The rate and extent of electromigration during programming of an electrical fuse is dependent on the temperature and the current density at the electromigrated portion.
An electrical fuse typically comprises an anode, a cathode, and a fuselink. The fuselink is a narrow strip of a conductive material adjoining the anode and cathode. During programming of the electrical fuse, a positive voltage bias is applied to the anode and a negative voltage bias is applied to the cathode. As electrical current flows through the fuselink having a narrow cross-sectional area, the temperature of the fuselink is elevated. A high current density combined with the elevated temperature at the fuselink facilitates electromigration of the conductive material which may comprise a metal silicide.
In general, the higher the temperature of the fuselink, the easier it is to electromigrate the conductive material, i.e., the less current is needed to induce electromigration. Since programming of electrical fuses typically takes a substantial amount of current, for example, a programming current of about 5 mA for an electrical fuse having a fuselink width of about 63 nm, it is advantageous to provide effective thermal isolation to the fuselink to keep the temperature of the fuselink elevated during the programming.
While fuselinks of conventional electrical fuses are insulated by dielectric materials so that heat loss from the fuselink is contained during programming of the electrical fuse, improved thermal isolation of the fuselink and a higher temperature during programming would reduce the amount of electrical current needed for programming the electrical fuse. Such a reduction in the electrical current needed for programming would allow reduction of the size of a programming transistor.
In view of the above, there exists a need for an electrical fuse structure having improved thermal isolation around a fuselink, and consequently requiring less programming current, and methods of manufacturing the same.